It is known that polymeric materials must be pretreated before chemical and subsequent electrolytic metallizing, for example by etching the polymer surface using chromic acids.
The polymer surface is altered during etching in such a way that caverns and vacuoles are formed. This is only possible with certain polymers, for example with 2-phase multi-component graft polymers or copolymers, such as ABS polymers, impact resistant polystyrene or 2-phase homopolymers, such as partially crystalline polypropylene.
Moreover, the application of chromic acid or other oxidants is associated with an impairment of the physical properties of the polymeric base material such as notched impact strength and electrical surface resistance.
Further, the hexavalent chromium which is drawn into the activation bath and into the metallizing bath causes these baths to be poisoned.
The same disadvantages are encountered in processes in which the polymer surface is chemically altered using a strong gaseous oxidant, for example hot SO.sub.3 vapour.
The conventional processes for non-electrical metallization of materials usually comprise relatively many process steps and also have the disadvantage that they are limited to substrates which may be chemically or physically roughened due to their physical form or chemical structure.
EP-A 0,081,129 further discloses that an activation which produces strongly adhering metallic coatings is achieved by "swelling adhesion nucleation." This elegant process has the disadvantage however that it causes stress cracking in complex shaped polymeric injection mouldings. Further, this process requires a new swelling activation system for each type of plastic and thus is not universally applicable.
Finally, US-A 3,560,257 and 4,017,265 and also DE-A 3,627,256 disclose processes for activation, which use activator solutions containing adhesion promoting polymers. The disadvantage of these processes is that they require the use of relatively high concentrations of expensive precious metal activators.
An object of the present invention was thus to develop an economic process for chemical metallizing, by which material surfaces based on all commercial plastics can be given a strongly adhering metallic coating deposited by wet chemical methods without previous etching with oxidants.
The object can be achieved by coating the substrate surfaces with a primer based on a polymeric organic film former.